People used levers already in ancient times, using them to move large weights with a relatively small force. In addition, the lever is the yoke of the scale, on which different loads can be balanced. Experience shows that in equilibrium the shoulders of the loads are inversely proportional to these loads. Archimedes proved this law using reasoning reminiscent of the proof of a geometric theorem. When calculating real levers, we must not forget that the lever itself also weighs something.